Effect of Cooling Rate on Transformation Plasticity of 0.45% Carbon Steel

Abstract

This study aims at investigating the effect of cooling rate on transformation plastic strain in 0.45 mass% carbon steel. It has been revealed that slow cooling rate increases the magnitude of transformation plastic strain especially at the cooling rate less than 10°C/s. Based on Greenwood-Johnson mechanism (strain accommodation mechanism), transformation plasticity modelling is made using crystal plasticity fast Fourier transform numerical method. It is shown that there are three inter-related mechanisms that control the amount of transformation plasticity as a function of cooling rate: the dependence of yield stress of weaker phase with temperature, the dependence of volume change to cooling rate (higher volume change at higher cooling rate) and the influence of viscoplasticity behaviour that enhances creep strain at high temperature. The model predicts the transformation plastic strain relatively close to those of experimental ones at high cooling rates (typically 10°C/s and above) where phase transformation happens at low temperatures, while it under estimates the transformation plastic strain at slow cooling rates where phase transformation happens at high temperatures. These results show that other mechanisms like creep/viscoplasticity should be considered by the model to predict influence of cooling rate on transformation induced plasticity.